Method for Energy Storage with Co-production of Peaking Power and Liquefied Natural Gas

ABSTRACT

A method for energy storage with co-production of peaking power and liquefied natural gas (LNG) which integrates the processes of liquid air energy storage and reduction in pressure of natural gas through expander at the co-located city gate station and includes consumption of excessive power from the grid, mechanical power of the natural gas expander and cold thermal energy of expanded natural gas for charging the storage with a liquid air during off-peak hours and production of peaking (on-demand) power by the expanders of natural gas and highly-pressurized re-gasified air with recovering the cold thermal energy of expanded natural gas and regasified liquid air for liquefying a part of delivered natural gas at the city gate station and energy storage facility.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefits of U.S. Provisional Application No.62/393,252 titled “Method for Energy Storage with Co-production ofPeaking Power and Liquefied Natural Gas” and filed on Sep. 12^(th) 2016.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTINGCOMPACT DISK APPENDIX

Not Applicable

FIELD OF INVENTION

The present invention relates to the field of energy conversiontechnique, and more specifically to the methods enabling an improvementin the technologies intended for conversion and storage of excessiveenergy and natural gas at the pressure reducing (city gate) stations.More particularly, the present invention relates to the methods makingpossible to profitably combine the operation of the small scale liquidair energy storage with co-production of liquefied natural gas (LNG)directly at the storage facility and at the co-located city gatestation.

BACKGROUND OF THE INVENTION

In modern times the electrical energy storages are becoming an integralpart of the distribution grids, ensuring the on-demand and reliablesupply of electricity by the intermittent renewable energy sources andproviding a stable and efficient operation of the base-load fossil-fuelfired and nuclear power plants around the clock.

Amongst the known methods for energy storage able to accumulate a lot ofenergy and store it over a long time-period, the recently proposedmethods for Liquid Air Energy Storage (LAES) (see e.c. Patent. FR2,489,411) are distinguished by a much simpler permitting process andthe freedom from any geographical, land and environmental constraints,inherent in other known methods for large-scale energy storagetechnologies, lice Pumped Hydro Electric Storage (PHES) and CompressedAir Energy Storage (CAES). In the LAES systems liquid air is producedusing excessive power from the grid, stored in the small volume tanksbetween the off-peak and on-peak hours and re-gasified and used aseffective working medium for producing a peaking power in the periods ofhigh power demand. However, producing a liquid air during off-peak hoursis an energy intensive process and many technical solutions have beenproposed for reducing the energy consumption and losses in this processwith an increase in the LAES round-trip efficiency.

One of the possible ways for improvement in performance of the LAESfacility could be its integration with the natural gas (NG) pressurereducing (city gate) station and recovery an available exergy of thehigh-pressure (HP) gas being presently wasted in the throttling valves.At the same time, the known proposals on utilization of available HP NGpotential can't be used for achievement of the invention goals for thefollowing reasons. Some of these proposals make possible to replace thethrottling valves by the turbo-expanders converting a kinetic energy ofthe motive gas stream into a “green” power. Therewith a thermal energyat a rate of ˜3.5 kWth per each kW of additional mechanical powerproduced should be consumed to provide the identical temperatures of thehigh-pressure and low-pressure gas streams, resulting in a lowefficiency of thermal energy-to-power conversion efficiency. Inaddition, recovery of wasted kinetic energy is desirable to perform onthe 24/7 basis, whereas the actual need for this power is arising onlyduring on-peak hours. Therefore, during off-peak hours it would beexpedient to recover the energy of gas expansion at the CG station fordesirable improvement in the performance of integrated LAES facility andto find the more effective ways for use of the mentioned thermal energy.

The other known proposals are devoted to using a high-pressure gaspotential for liquefaction of a part of delivered gas at the CG stations(Tianbiao He and Y. L. Ju “A novel process for small-scale pipelinenatural gas liquefaction”, Applied Energy, No. 115, pp. 17-24, Febeuary2014). This makes possible to store and on-demand use the LNG produced,flattening the fluctuations in NG supply caused by daily and seasonalvariations in flow and pressure of natural gas at the CG station inletand outlet. Alternatively the LNG may be distributed as a transport fuelat the adjacent filling stations. In these proposals the whole of theavailable energy of high-pressure gas stream recovered in theturbo-expanders is spent for increase in the LNG production rate ratherthan delivering a produced power into the grid. In addition, a proposedLNG production at the CG station is characterized by a very low gasliquefaction ratio. Because of this, the integration between the CGstation and LAES facility could make possible to use a high cold thermalenergy potential of re-gasified liquid air for increase in common LNGproduction at the station and facility on the one hand and to provide apeaking power production capability of the CG station on the other hand.

As a whole, the method for energy storage with co-production of peakingpower and liquefied natural gas is selected as a subject for aninnovative improvement in the present invention. Thereby, theintegration between the liquid air energy storage and CG station withexchange and recovery of the waste energy streams of the integratedfacilities are found to be the effective means for achievement of theinvention's goals.

SUMMARY OF THE INVENTION

In one or more embodiments, a proposed method for energy storage withco-production of peaking power and liquefied natural may comprise incombination: a) charging the energy storage facility with liquid airproduced through consumption of an excessive power from the grid and/orany co-located energy source; b) discharging the energy storage facilitythrough expanding the re-gasified air with on-demand producing anddelivering a peaking power to the grid; and c) reducing a pressure ofnatural gas at the co-located city gate station from a high inlet valuedown to a low outlet one with co-producing the LNG from a part ofsupplied gas through usage of auto-refrigeration of expanded gas stream.

The invented method may differ from the known those in that: a)depressurizing a gas at the said city gate station may be performed withproducing a power which may be used for at least partial meeting thedemands for power during charging the energy storage facility and may bedelivered into grid during discharging the energy storage facility; b)co-producing the LNG at the said city gate station during charging theenergy storage facility may be supplemented by simultaneous re-gasifyingthe whole of LNG produced and using a released cold thermal energy forreducing the facility demands for a power consumed; and) c) producing apeak power during discharging the energy storage facility may besupplemented by a simultaneous using a cold thermal energy of there-gasified air stream for co-producing the LNG directly at the facilityfrom a part of gas delivered to the city gate station.

In one or more embodiments, charging the energy storage facility withliquid air may include the steps of: a) externally powered compressingthe fresh air stream up to a bottom charge pressure with its furtherfreeing from the CO₂ and H₂O contaminants; b) mixing the streams oftreated fresh and recirculating air streams at a bottom charge pressurethus forming a process air stream; c) succeeding externally poweredcompressing the process air up to a rated charge pressure; d) finalself-powered compressing the whole air stream air by at least onebooster compressor driven by a cold turbo-expander of open airauto-refrigeration cycle; and e) further processing the process airbetween the top and bottom charge pressures in the said airauto-refrigeration cycle, resulting in generating a liquefied air from apart of process air at a bottom charge pressure and recirculating a restof it for mixing with a fresh air; and may further be characterized by:a) providing at least a part of external power required for compressingthe fresh and process air at the sacrifice of power produced at theco-located city gate station in the process of gas depressurization; andb) providing a deep cooling of the recirculating air stream before itsmixing with a fresh air at the sacrifice of cold thermal energy releasedin the process of LNG re-gasification.

In one or more embodiments, discharging the energy storage facility witha peaking power production may further include the steps of: a) pumpingthe liquid air at a top discharge pressure; b) re-gasifying the pumpedair with capturing its cold thermal energy; and c) expanding are-gasified air down to bottom discharge pressure in at least one-stageexpander with on-demand producing the bulk of peaking power; and mayfurther be characterized by: a) providing a co-production of the LNGdirectly at the energy storage facility in addition to the bulk of LNGproduction at the city gate station at the sacrifice of harnessing acaptured cold thermal energy in the process of liquefying the whole ofnatural gas delivered from the said station; and b) providing a thermalassistance to the air expanding process through an increase in airtemperature upstream of each expansion stage at the sacrifice of thermalenergy derived from any available source of such energy and selectedfrom the group comprising but not limited to ambient air, industrialwaste heat streams, and combusting a part of depressurized natural gasescaping city gate station.

In one or more embodiments, reducing a pressure of natural gas from ahigh inlet value down to a low outlet one at the co-located city gatestation during charging the energy storage facility may further includethe steps of: a) pre-cooling the whole of delivered high-pressure gaswith a stream of low-pressure gas escaping the said station; b) dividinga pre-cooled high-pressure gas into two streams, first of which isfurther used for liquefaction of the second one in the openauto-refrigeration cycle; c) succeeding deep cooling and liquefying thesecond gas stream with a stream of low-pressure gas escaping the citygate station; d) expanding the second liquefied gas stream down to asaid low gas pressure accompanied by final cooling the expandedtwo-phase stream down to the bottom cycle temperature; and e) separatingthe liquid and vapor phases of the second gas stream, resulting informing the liquefied part and vapor part of a said stream at a said lowgas pressure; and may further be characterized by: a) pumping aliquefied part of the second gas stream up to a said high pressure atwhich gas is delivered into city gate station; b) exchanging thermalenergy between a recirculating air stream from the energy storagefacility and a pumped liquefied part of the second gas stream from thecity gate station, resulting in said deep cooling a recirculating airstream before its mixing with a stream of treated fresh air and inre-gasifying a pumped part of the second gas stream; c) mixing the firstgas stream and a re-gasified part of the second gas stream at a saidhigh gas pressure; d) expanding the mixed gas stream down to a said lowgas pressure accompanied by producing a power and deep cooling the saidmixed gas stream down to the bottom cycle temperature; e) using a powerproduced by the expanded mixed gas stream at the city gate station as atleast a part of external power required for compressing the fresh andprocess air at the energy storage facility; f) blending the expandedmixed gas stream with a vapor part of the second gas stream so forming astream of low-pressure gas escaping the city gate station; and g) usinga cold thermal energy of low-pressure gas stream escaping the city gatestation for the said deep cooling and liquefying the second gas streamand pre-cooling the whole of delivered high-pressure gas.

In one or more embodiments, reducing a pressure of natural gas from ahigh inlet value down to a low outlet one at the co-located city gatestation during discharging the energy storage facility may furtherinclude the steps of a) pre-cooling the whole of delivered high-pressuregas with a stream of low-pressure gas escaping the said station; b)dividing a pre-cooled high-pressure gas into two streams, first of whichis further used for liquefaction of the second one in the openauto-refrigeration cycle; c) succeeding deep cooling and liquefying thesecond gas stream with a stream of low-pressure gas escaping the citygate station; d) expanding the second liquefied gas stream down to asaid low gas pressure accompanied by final cooling the expandedtwo-phase stream down to the bottom cycle temperature; e) separating theliquid and vapor phases of the second gas stream, resulting in formingthe liquefied part and vapor part of a said stream at a said low gaspressure; and f) using a liquefied part of the second gas stream as thebulk of LNG produced and stored at a pressure identical to a lowpressure of gas escaping the city gate station; and may further becharacterized by: a) expanding the first gas stream down to a said lowgas pressure accompanied by producing a power and deep cooling the saidfirst gas stream down to the bottom cycle temperature; b) using a powerproduced by the expanded first gas stream at the city gate station asaddition to a peaking power on-demand delivered to the grid by theenergy storage facility; c) blending the expanded first gas stream witha vapor part of the second gas stream so forming a stream oflow-pressure gas escaping the city gate station; and d) using a coldthermal energy of low-pressure gas stream escaping the city gate stationfor the said deep cooling and liquefying the second gas stream andpre-cooling the whole of delivered high-pressure gas.

In one or more embodiments, a temperature of low-pressure gas escapingthe city gate station during charging the energy storage facility may beincreased up to at least permissible minimum through a heat exchangebetween a stream of process air escaping the externally poweredcompressor train and a stream of low-pressure gas escaping the city gatestation.

In one or more embodiments, producing the LNG at the city gate stationduring discharging the energy storage facility at a pressure level belowa said low pressure of gas escaping the station may include theadditional steps of: a) reducing a pressure of liquefied part of thesecond gas stream down to a required level accompanied by formation of atwo-phase stream; b) separating a liquid phase from the two-phase streamwith its storing and on-demand delivering as a salable LNG product at arequired pressure; c) compressing a vapor phase of the two-phase streamup to a low gas pressure at the city gate outlet or up to a high gaspressure at the station inlet; and d) mixing the compressed vapor streamwith a low-pressure gas escaping the station or with a high-pressure gasdelivered to the station.

In one or more embodiments, a high-pressure gas at the inlet of citygate station may be on-demand dried and ridded of the water vapor andcarbon dioxide contaminants upstream of the pre-cooling step.

Finally, in one or more embodiments a natural gas delivered into citygate station may be on-demand subjected to freeing from the contaminantsincluding the steps of: a) drying the whole of high-pressure gasupstream of the pre-cooling step; b) removing the liquefied and/orsolidified CO₂ contaminants from the first gas stream downstream of theexpanding step; and c) removing the CO₂ contaminants from the second gasstream upstream of the deep cooling and liquefying step.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will hereinafter be described in detail below with referenceto the accompanying drawings, wherein lie reference numerals representlike elements. The accompanying drawings have not necessarily been drawnto scale. Where applicable, some features may not be illustrated toassist in the description of underlying features.

FIG. 1 is a schematic view of the first embodiment for implementing thecharge of energy storage with recovery of wasted energy flows from theintegrated city gate (CG) station, according to the present invention.

FIG. 2 is a schematic view of the second embodiment for implementing thedischarge of energy storage with recovery of wasted energy flow of theintegrated liquid air energy storage (LAES) facility, according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The practical realization of the proposed method for energy storage withco-production of breaking power and liquefied natural gas (LNG) may beperformed through the operational interaction between the integratedLAES facility and CG station both during storage charge and discharge.FIG. 1 shows schematically the first embodiment for implementing thecharge of energy storage with recovery of wasted energy flows from theintegrated CG station. Here the involved equipment packages are designedas:

100—compressor train of the LAES facility

200—turbo-expander-booster compressor train of the LAES facility

300—liquefaction, separation and storage equipment of the LAES facility

400—equipment package of the CG station.

According to the present invention, compressor train is designed astwo-stage turbomachinery, wherein the first compression stage 102 andsecond compression stage 106 are driven by the common electric motor103. A fresh air from atmosphere is delivered through a pipe 101 intothe first compression stage 102 and pressurized up to a bottom chargepressure. Train is equipped with intercooler 104 and inter-cleaner(adsorber) 105 for capture of moisture and carbon dioxide from apressurized fresh air. A removal of compression heat in the intercooler104 may be performed by an ambient air or water. At the outlet ofadsorber (point 107) the cooled and cleaned fresh air is mixed with arecirculating air stream 315 delivered under a bottom charge pressurefrom a package 300 through a package 400, so forming a process airstream 108, which is further compressed in the second compression stage106 up to a rated pressure level. During deep cooling a recirculatingair stream 315 in the heat exchanger 406 its temperature drops below−100° C., resulting in corresponding drastic decrease in temperature ofthe mixed air stream 108 upstream of compressor 106 and in powerconsumed by this compressor. The said deep cooling of recirculating airis performed with a stream of the LNG produced at the city gate station,as described below. Removal of compression heat from a process airescaping the compressor 106 with cooling the air down to −5° C.-−15° C.is performed in the heat exchanger 109 by a stream of low pressure gasescaping the city gate station, as also described below.

Further compressing the entire process air stream up to a top chargepressure is performed in the booster compressor 201 driven by the coldturbo-expander 202 with cooling the air after said compressor in theheat exchanger 203. At given ratio between the top and bottom chargepressures, the mentioned marked cooling the process air at the inlet ofbooster compressor 201 makes possible to increase a pressure ratio inthis compressor without increase in power consumed by it. In its turn,this provides a corresponding decrease in a pressure ratio in thecompressor 106, resulting in a further reducing a power consumed by it.

At the said top charge pressure the process air stream is delivered intoa deep cooler 301, wherein its temperature decreased substantially below0° C. with a recirculating air stream. Further air is directed to thepoint 302, wherein it is divided into two streams 303 and 305. Theextracted part of process air (stream 303) is expanding down to a bottomcharge pressure in the said cold turbo-expander 202 with an accompanieddeep cooling of expanded air stream 304. The rest of process air (stream305) is additionally cooled and fully liquefied with a recirculating airin the air liquefier 306. The liquefied rest of process air is furtherdirected into a generator-loaded turbine 307, wherein it is expandeddown to a bottom charge pressure with an accompanied final cooling ofexpanded air down to bottom charge temperature. A bottom charge pressureis selected at a level exceeding atmospheric pressure by 1-7 bar. An airseparator 308 installed at the outlet of expander 307 is used toseparate the liquid and vapor phases of the finally expanded and cooledrest of process air. The liquid air stream 309 is directed to thepressurized liquid air vessels 310, wherein it is stored at The bottomcharge pressure and temperature between the energy storage charge anddischarge. The air vapor stream 311 is directed to the point 312,wherein its mixing with an expanded and cooled part 304 of process airis performed. This results in formation of a recirculating air stream313 at a bottom charge pressure. The said recirculating air stream isfurther used for the final cooling and liquefying the rest 305 ofprocess air in the air liquefier 306, causing the accompanied heatingthe outgoing stream 314 of recirculating air. This air stream is furtherused for said cooling the process air in the deep cooler 301, causingthe accompanied further heating the outgoing stream 315 of recirculatingair. As mentioned above, the recirculating air stream 315 escaping thepackage 300 is deeply cooled in the heat exchanger 417 before its mixingwith a fresh air stream at the point 107.

Operation of the integrated CG station during energy storage charge isrun as follows. The stream of natural gas at a rated high-pressure (HP)is delivered from the main pipeline through a pipe 401 into adsorber402, wherein it is cleaned of the water vapor and carbon dioxidecontaminants. The cleaned gas is subjected to pre-cooling in the heatexchanger 403 with a stream of natural gas escaping the city gatestation and directed further to the cold turbo-expander 404shaft-connected with the generator 405. Power produced by thecold-turbo-expander through recovery of the wasted gas pressure dropcomprises from 50 to 100% of energy required for driving the compressortrain, depending on the pressure ratio in the expander 404. In so doing,the electric motor 103 of compressor train takes its current from thegenerator 405 only or from the electric grid and generator 405 at onetime. The expanding of gas down to a rated low pressure is accompaniedby its deep cooling down to a bottom cycle temperature, at which gas isdelivering to the said heat exchanger 406, wherein its cold thermalenergy is used for a deep cooling of the recirculating air stream 315,as described above. The low-pressure gas escaping the heat exchanger 406possesses a yet sufficient cold thermal energy to pre-cool the incomingstream of high-pressure gas in heat exchanger 403 and intercool theprocess air in the heat exchanger 109 between the second stage 106 ofcompressor train and the booster compressor 201. Resulting from a heatexchange in the said equipment, the stream of low-pressure gas 407 isdelivered into a low-pressure main pipeline at a temperature equal to orexceeding a minimum allowable value.

FIG. 2 shows schematically the second embodiment for implementing thedischarge of energy storage with recovery of wasted energy flow of theintegrated LAES facility. Here the involved equipment packages aredesigned as:

300—liquefaction, separation and storage equipment of the LAES facility

400—equipment package of the CG station

500—LNG production package of the LAES facility

600—expander train of the LAES facility.

Operation of the LAES facility in discharge operation mode is performedas follows. A stream 315 of liquid process air is extracted at a bottomdicharge pressure from the storage 310 and pumped by a pump 316 up totop discharge pressure selected in the range between 10 and 200 bar. Thedischarged air stream 317 is delivered into a package 500 which isdestined for liquefaction of a stream of high-pressure natural gas 423supplied from a CG station package 400. The feed gas destined forliquefaction at the LAES facility is dryed and purified at the said CGstation and is pressure is consistent with a high pressure of gas intoCG station from the main HP pipeline. At the LNG production pressureselected in the range between 2 and 12 barA a flow-rate of the LNGproduced at the LAES facility may reach 15-55% of a flow-rate ofdischarged air flow-rate. As this takes place, a LNG production yieldmay be somewhat increased through a decrease in selected top dischargedair pressure at a given high pressure of supplied natural gas. Forrealization of this approach the appropriate adjustment of the liquidair pump 316 and selection of a proper expander train 600 configurationare required.

To provide the LNG production directly at the LAES facility a pumpeddischarged air stream 317 is delivered into a gas liquefier—airregasifier 501. Exchange of thermal energy between the discharged liquidair and supplied natural gas in this heat exchanger results inliquefaction of entire gas stream 423 and regasification of entiredischarged air stream 317. The latter is directed from the regasifier501 to the air expander train 600, wherein it first preheated in therecuperator 601, and thereafter superheated in the heat exchanger 602 ata sacrifice of heat exchange with a stream 608 of thermal (preferablywasted) energy. The following expanding the superheated air stream isperformed in the at least one-stage expander train 600 whoseconfiguration is selected with regard to a top discharged air pressureprovided by a pump 316. At a said pressure exceeding 40-45 barA atwo-stage expander train configuration with reheating a discharged airbetween the stages may be used.

As shown in the FIG. 2, the superheated air is expanded in the firststage 603 of expander train and reheated in the heat exchanger 604 at asacrifice of heat exchange with a stream 607 of thermal (preferablywasted) energy. In its turn, the reheated air stream is expanded down toa bottom discharge pressure near atmospheric with an accompanied itscooling at the outlet of stage 605. A work performed by the expanded airstream in the stages 603 and 605 is converted into electric power by theshaft-coupled generator 606. A process air escaping the second stage 605of expander train possesses a sufficient thermal energy to be used inthe recuperator 601 for the said preheating a discharged air upstream ofthe superheater 602.

A liquefied natural gas is directed from the heat exchanger 501 to thegenerator-loaded liquid gas expander 502, wherein its depressurizationdown to a selected storage pressure with a final cooling are performed.This results in forming the LNG product which is stored in thepressurized storage tank 503 and on-demand delivered to the customers.

Operation of the integrated CG station during energy storage dischargeis run as follows. The stream of natural gas at a rated high-pressure(HP) is delivered from the main pipeline through a pipe 401 intoadsorber 402, wherein it is cleaned of the water vapor and carbondioxide contaminants. At the adsorber outlet (point 408) a small part424 of cleaned gas is extracted and directed to a package 500 for itsfull liquefaction directly at the LAES facility as described above,whereas the bulk of cleaned gas is subjected to pre-cooling in the heatexchanger 403 with a stream of natural gas escaping the city gatestation. At the point 409 the gas stream is divided into parts. Thefirst (greater) part is directed to the generator 405-loaded coldturbo-expander 404, wherein it is expanded down to a rated low pressure(LP) and deeply cooled. A power produced by the cold expander 404depends on a pressure ratio in it and may be comparable to a powerproduced by the hot expander train of the LAES facility operated withreasonable superheating and reheating of discharged air stream.

The second (lesser) part of the HP gas is subjected to deep cooling andliquefying in the heat exchanger 410 with a following expansion in theliquid gas expander 411 down to a said rated low pressure. The two-phasegas stream escaping the expander 411 is separated into a liquid phase(properly LNG) and vapor phase in the separator 412. The latter iscombined at the point 413 with a stream of gas escaping the expander404, forming the combined gas stream 414 at a bottom cycle temperatureand a rated low pressure. The combined LP gas stream sequentially passesthrough the liquefier 410 and pre-cooler 403, providing accordingly theliquefaction of the said second part of natural gas and pre-cooling thewhole of the gas delivered into CG station. Resulting from a heatexchange in the said equipment, the stream of low-pressure gas 415 isdelivered into a low-pressure main pipeline at a temperature equal to orexceeding a minimum allowable value.

A further processing of the LNG produced at the CG station is performedin accordance with a pressure of the LNG storage. If a pressure ofpressurized LNG in the tank 503 is equal to a said rated low pressure ofnatural gas, the produced LNG is directly delivered from a separator 412into a storage vessel 503 through the open valve 416 and pipe 417 withthe closed valve 418. If a pressure of pressurized LNG in the tank 503is below a said rated low pressure of natural gas, the produced LNG isdirected from a separator 412 through the open valve 418 with the closedvalve 416 to a Joule-Thomson valve 419, wherein its pressure reduceddown to a pressure in the storage tank 503. A gas separator 420installed at the outlet of JT valve 419 is used to separate the liquidand vapor phases of the partially depressurized gas stream. A greater(liquid) gas stream 417 is directed to the pressurized liquid gas vessel503, whereas a minor (vapor) gas stream 421 is compressed up to a ratedlow gas pressure by the auxiliary compressor 422 and directed through apipe 423 to the LP gas distribution grid. As a whole, amount of the LNGproduced directly at the LAES facility makes up between 25% and 45% ofthe LNG production rate at the CG station.

INDUSTRIAL APPLICABILITY

The performance of small-scale energy storage with co-production ofpeaking power and liquefied natural gas (LNG) are presented below. Thecalculation of these performances has been performed as applied tointegration between liquid air energy storage (LAES) facility and citygate (CG) station. The latter is exemplified by CG station designed forreducing a pressure of the ˜43,000 m³/h of natural gas (assumed as 100%of methane) from 75 barA down to 15 barA (Alt.1), from 65 barA down to 7barA (Alt.2) and from 25 barA down to 5 barA (Alt. 3). During LAEScharge the whole of obtained gas is delivered from the CG station into alow-pressure gas distribution pipeline, whereby mechanical energy of theexpanded gas and its cold thermal energy are recovered at the LAESfacility, reducing consumption of external power required for airliquefaction. During LAES discharge from 15 to 30% of obtained gas isliquefied at the CG station and LAES facility, resulting in theircombined LNG capacity between 0.02 and 0.03 MTPA. The rest of obtainedgas is delivered to the customers at the reduced pressure.Simultaneously mechanical energy of the gas expanded at the CG stationand re-gasified air expanded at the LAES facility is converted into1.3-1.6 MWe of peaking power delivered into electric grid.

In the conducted feasibility study it was assumed that the LAES facilityis equipped with the equipment, providing its charge with use of singleturbo expander-compressor based open air auto-refrigeration cycle (seeFIG. 1) and its discharge with use of Thermally assisted 2-stageexpander (see FIG. 2) recovering waste heat of the co-located energysource or heat from combustion of small amount of depressurized fuel.Operation of the CG station is performed with use of one coldturbo-expander and a package of cold energy recovery equipment, as shownin FIGS. 1 and 2.

The given and assumed technical data used in numerical simulation of theenergy storage performance are listed in the Table 1 below.

TABLE 1 Parameter Unit Data Diapason of combined peaking power of theMWe 1-2 LAES facility and CG station Daily duration of the LAES chargeand discharge h 12/12 Total compressor polytropic & mechanicalefficiency % 87 Total expander adiabatic & mechanical efficiency % 87Total coupling & electric motor efficiency of % 97 turbomachineryIsentropic liquid air and gas expander efficiencies % 85 Isentropicliquid air pump efficiency % 80 Small generator/motor electricefficiency % 96 Compressor train outlet pressure barA 37.1 Top chargepressure barA 61.7 Bottom charge pressure barA 6.7 Top dischargepressure barA 150 Pressure ratio in HP and LP air expanders 12.5 Assumedpressure drop in piping barA 0 Assumed pressure drop in each heatexchanger barA 0.025 Discharged air temperature at HP and LP expandersinlet ° C. 565 HP natural gas inlet pressure vs. selected AlternativebarA 75-25 LP natural gas outlet pressure vs. selected Alternative barA15-5  Pressure of LNG produced vs. Alternative barA 7-5

In their turn, the main calculated performance of the integrated LAESfacility and CG station during LAES charge are presented in the Table 2.Here the following designations are used: G_(PA) and G_(LA)−flow-ratesof process air and liquid air produced; W_(FAC) and W_(MAC)−mechanicalpower consumed by the feed and main air compressors;W_(LAES-CH)−electric power consumed by the LAES facility;ALR=(G_(LA)/G_(PA))×100%−air liquefaction ratio; G_(HPG) andG_(LPG)−flow-rates of HP gas delivered into CG station and LP gasescaping CG station; P_(HP)−high pressure of gas delivered into CGstation; P_(LP)−low pressure of gas escaping CG station;W_(CTE)−electric power produced by cold turbo-expander of the CGstation; W_(CH)=W_(LAES-CH)−W_(CTE)−total electric power consumed fromthe grid during LAES charge; and ω_(CH)=W_(CH)/(G_(LA)×3.6)−specificexternal power consumed for air liquefaction during LAES charge.

TABLE 2 Parameters Unit Alternative 1 Alternative 2 Alternative 3 CITYGATE STATION P_(HP) barA 75 65 25 P_(LP) barA 15 7 5 G_(HPG) kg/s 7.627.62 7.62 G_(LPG) kg/s 7.62 7.62 7.62 W_(CTE) kWe 755 1,023 916 LAESFACILITY G_(PA) kg/s 6.58 6.58 6.58 G_(LA) kg/s 1.0 1.0 1.0 W_(FAC) kWm256 256 256 W_(MAC) kWm 927 802 936 W_(LAES-CH) kWe 1,214 1,085 1,223ALR % 15.2 15.2 15.2 TOTAL CHARGE W_(CH) kWe 459 62 307 ω_(CH) kWh/ton128 17 79

The main calculated performance of the discharge process and combinedoperational results are presented in the Table 3, wherein the followingdesignations are used: G_(HPG) and G_(LPG)−flow-rates of HP gasdelivered into CG station and LP gas escaping CG station; G_(LNG-CG),G_(LNG-LAES) and G_(LNG)=G_(LNG-CG)+G_(LNG-LAES)−flow-rates of LNGproduced correspondingly at the CG station, LAES facility and incombination; GLR=(G_(LNG)/G_(HPG))×100%−gas liquefaction ratio;P_(HP)−high pressure of gas delivered into CG station; P_(LP)−lowpressure of gas escaping CG station; P_(LNG)−pressure of the producedLNG; W_(CG)−electric power produced by the CG station; Q_(TH-SH) andQ_(TH-RH)−thermal load of air superheater and reheater; W_(HPAE) andW_(LPAE)−mechanical power produced by the high and low pressure airexpanders; W_(LAES-DCH)−electric power produced by the LAES facility;ω_(LAES-DCH)=W_(LAES-DCH)/(G_(LA)×3.6)−specific power produced duringLAES facility discharge; RTE_(GRID)=(W_(LAES-DCH)/W_(CH))×100%−gridround trip efficiency of the LAES facility; andW_(DCH)=W_(LAES-DCH)+W_(CG)−total electric power delivered into the gridduring LAES discharge.

As may be seen from the data presented in the Tables 2 and 3, theproposed integration of the LAES facility and CG station provides adrastic decrease in consumption of external power during LAES charge andmultifold return of the power into grid during LAES discharge throughoutthe entire diapasons of the gas pressure ratio (π=P_(HP)/P_(LP)) andinlet gas high pressure P_(HP), at which natural gas enters the CGstation. Particularly high RTE_(GRID) values may

TABLE 3 Parameters Unit Alternative 1 Alternative 2 Alternative 3 CITYGATE STATION P_(HP) barA 75 65 25 P_(LP) barA 15 7 5 G_(HPG) kg/s 8.078.07 8.02 G_(LPG) kg/s 6.19 5.82 6.67 G_(LNG-CG) kg/s 1.43 1.8 0.95P_(LNG) barA 7 7 5 W_(CG) kWe 614 838 562 LAES FACILITY G_(LA) kg/s 1.01.0 1.0 Q_(TH-SH) kWth 430 430 430 Q_(TH-RH) kWth 384 384 384 W_(HPAE)kWm 390 390 390 W_(LPAE) kWm 385 385 385 W_(LAES-DCH) kWe 736 736 736ω_(LAES-DCH) kWh/ton 204 204 204 RTE_(GRID) % 160 1192 239 G_(LNG-LAES)kg/s 0.45 0.45 0.4 TOTAL DISCHARGE AND SUMMARY W_(DCH) kWe 1,350 1,5731,297 Annual Capacity kWh/ton 5,346 6,229 5,136 G_(LNG) ton/h 6.8 8.14.9 ton/y 26,801 32,076 19,246 GLR % 23.3 27.9 16.8be achieved at the enhanced gas pressure ratio, as it is in AlternativeC at the π=9.3. However, most of the CG stations are using the lessergas pressure ratio, allowing nonetheless the impressive RTE_(GRID)values to be attained, as in the Alternatives A and C, wherein at theπ=5 RTE_(GRID) values are equal to 160% and 240% correspondingly.

The recent developments in the field of pressure reducing stations haveresulted in introducing the natural gas turbo-expanders into theirdesign, making possible to recover a wasted mechanical power of expandedgas for generation of so-called “green” power. Such the turbo-expandersshould be equipped with a mandatory pre-heaters of the high-pressure gasto provide a minimum admissible gas temperature in the low pressurepipelines identical to that in the high pressure pipeline. On the onehand, preheating a gas upstream of “warm” turbo-expander increases itsoutput, but on the other hand an extra power is generated with a lowthermal energy-to-power conversion efficiency, not exceeding 30%. In thepresent invention a “warm” turbo-expander is replaced by a “cold” one,wherein inlet temperature of dehumidified natural gas should besustained at a level significantly below 0° C. A thermal energy beingbefore used for pre-heating the natural gas may be now harnessed forsuperheating and reheating the expanded air at the LAES facility.Thereby an amount of thermal energy required in this case may be reducedby a factor of 2-3, whereas efficiency of its conversion into additionalpower of the air expander train may achieve 63-67%.

As also evident from the Tables 2 and 3, an amount of LNG produceddirectly at the LAES facility (G_(LNG-LAES)) is varied within narrowlimits (0.4-0.45 kg/s) for all considered alternatives, but its share ina total amount of LNG produced (G_(LNG)) varies over a wider range from20 to 30%. This is explained by a strong effect of two factors (gaspressure ratio in the cold turbo-expander and a value of inlet highpressure, at which natural gas enters the CG station) on the LNGproduction rate (G_(LNG-CG)) of this station. Thereby the second factormakes a greater impact on the G_(LNG-CG) value that must be consideredin the integration of the CG station with the LAES facility. Forexample, design of the CG stations in the alternatives A and C providesthe same gas pressure ratio (π=P_(HP)/P_(LP)=5) in the coldturbo-expanders, which however operate at the drastically distinct inlethigh pressures (75 barA for Alt. A and 25 barA for Alt. C). This willcause the value of G_(LNG-CG) in the Alt. A to increase by a factor of1.5 up to 1.43 kg/s, as compared to LNG production of 0.95 kg/s in theAlt. C. At the same time, design of the CG stations in the alternativesA and B provides the comparable levels of the gas inlet high pressure(75 barA for Alt. A and 65 barA for Alt. B), which however operate atthe drastically distinct gas pressure ratio in the cold turbo-expanders(π=5 for Alt. A and π=9.3 for Alt. B). This will cause the value ofG_(LNG-CG) in the Alt. B to increase only by a factor of 1.26 up to 1.8kg/s, as compared to LNG production of 1.43 kg/s in the Alt. A. As awhole, it should be noted that a total gas liquefaction ratio at theintegrated CG and LAES facility, varied in the range from 17 to 28%,significantly exceeds this value of the competitive technologies and maybe achieved with use of the simplest and cheap single expander-basedcycles for air and natural gas. Finally, the CG station with the highervalues of the inlet gas pressure (P_(HP)) and pressure ratio (π) in thecold turbo-expanders are preferable for integration with the LAESfacilities.

It should be noted that the term “comprising” does not exclude otherelements or steps and “a” or “an” do not exclude a plurality. It shouldalso be noted that reference signs in the claims should not apparent toone of skill in the art that many changes and modifications can beeffected to the above embodiments while remaining within the spirit andscope of the present invention.

What is claimed as new is:
 1. A method for energy storage withco-production of peaking power and liquefied natural gas (LNG),comprising in combination: charging the energy storage facility withliquid air produced through consumption of an excessive power from thegrid and/or any co-located energy source; discharging the energy storagefacility through expanding the re-gasified air with on-demand producingand delivering a peaking power to the grid; and reducing a pressure ofnatural gas at the co-located city gate station from a high inlet valuedown to a low outlet one with co-producing the LNG from a part ofsupplied gas through usage of auto-refrigeration of expanded gas stream;and wherein the improvement comprises in combination: depressurizing agas at the said city gate station is performed with producing a powerwhich is used for at least partial meeting the demands for power duringcharging the energy storage facility and is delivered into grid duringdischarging the energy storage facility; co-producing the LNG at thesaid city gate station during charging the energy storage facility issupplemented by simultaneous re-gasifying the whole of LNG produced andusing a released cold thermal energy for reducing the facility demandsfor a power consumed; and producing a peak power during discharging theenergy storage facility is supplemented by a simultaneous using a coldthermal energy of the re-gasified air stream for co-producing the LNGdirectly at the facility from a part of gas delivered to the city gatestation.
 2. A method as in claim 1, wherein charging the energy storagefacility with liquid air includes the steps of: a) externally poweredcompressing the fresh air stream up to a bottom charge pressure with itsfurther freeing from the CO₂ and H₂O contaminants; b) mixing the streamsof treated fresh and recirculating air streams at a bottom chargepressure thus forming a process air stream; c) succeeding externallypowered compressing the process air up to a rated charge pressure; d)final self-powered compressing the whole air stream air by at least onebooster compressor driven by a cold turbo-expander of open airauto-refrigeration cycle; and e) further processing the process airbetween the top and bottom charge pressures in the said airauto-refrigeration cycle, resulting in generating a liquefied air from apart of process air at a bottom charge pressure and recirculating a restof it for mixing with a fresh air; and is characterized by: providing atleast a part of external power required for compressing the fresh andprocess air at the sacrifice of power produced at the co-located citygate station in the process of gas depressurization; and providing adeep cooling of the recirculating air stream before its mixing with afresh air at the sacrifice of cold thermal energy released in theprocess of LNG re-gasification.
 3. A method as in claim 1, whereindischarging the energy storage facility with a peaking power productionincludes the steps of: a) pumping the liquid air at a top dischargepressure; b) re-gasifying the pumped air with capturing its cold thermalenergy; and c) expanding a re-gasified air down to bottom dischargepressure in at least one-stage expander with on-demand producing thebulk of peaking power; and is characterized by: providing aco-production of the LNG directly at the energy storage facility inaddition to the bulk of LNG production at the city gate station at thesacrifice of harnessing a captured cold thermal energy in the process ofliquefying the whole of natural gas delivered from the said station; andproviding a thermal assistance to the air expanding process through anincrease in air temperature upstream of each expansion stage at thesacrifice of thermal energy derived from any available source of suchenergy and selected from the group comprising but not limited to ambientair, industrial waste heat streams, and combusting a part ofdepressurized natural gas escaping city gate station.
 4. A method as inclaims 1 and 2, wherein reducing a pressure of natural gas from a highinlet value down to a low outlet one at the co-located city gate stationduring charging the energy storage facility includes the steps of a)pre-cooling the whole of delivered high-pressure gas with a stream oflow-pressure gas escaping the said station; b) dividing a pre-cooledhigh-pressure gas into two streams, first of which is further used forliquefaction of the second one in the open auto-refrigeration cycle; c)succeeding deep cooling and liquefying the second gas stream with astream of low-pressure gas escaping the city gate station; d) expandingthe second liquefied gas stream down to a said low gas pressureaccompanied by final cooling the expanded two-phase stream down to thebottom cycle temperature; and e) separating the liquid and vapor phasesof the second gas stream, resulting in forming the liquefied part andvapor part of a said stream at a said low gas pressure; and ischaracterized by: pumping a liquefied part of the second gas stream upto a said high pressure at which gas is delivered into city gatestation; exchanging thermal energy between a recirculating air streamfrom the energy storage facility and a pumped liquefied part of thesecond gas stream from the city gate station, resulting in said deepcooling a recirculating air stream before its mixing with a stream oftreated fresh air and in re-gasifying a pumped part of the second gasstream; mixing the first gas stream and a re-gasified part of the secondgas stream at a said high gas pressure; expanding the mixed gas streamdown to a said low gas pressure accompanied by producing a power anddeep cooling the said mixed gas stream down to the bottom cycletemperature; using a power produced by the expanded mixed gas stream atthe city gate station as at least a part of external power required forcompressing the fresh and process air at the energy storage facility;blending the expanded mixed gas stream with a vapor part of the secondgas stream so forming a stream of low-pressure gas escaping the citygate station; and using a cold thermal energy of low-pressure gas streamescaping the city gate station for the said deep cooling and liquefyingthe second gas stream and pre-cooling the whole of deliveredhigh-pressure gas.
 5. A method as in claims 1 and 3, wherein reducing apressure of natural gas from a high inlet value down to a low outlet oneat the co-located city gate station during discharging the energystorage facility includes the steps of: a) pre-cooling the whole ofdelivered high-pressure gas with a stream of low-pressure gas escapingthe said station; b) dividing a pre-cooled high-pressure gas into twostreams, first of which is further used for liquefaction of the secondone in the open auto-refrigeration cycle; c) succeeding deep cooling andliquefying the second gas stream with a stream of low-pressure gasescaping the city gate station; d) expanding the second liquefied gasstream down to a said low gas pressure accompanied by final cooling theexpanded two-phase stream down to the bottom cycle temperature; e)separating the liquid and vapor phases of the second gas stream,resulting in forming the liquefied part and vapor part of a said streamat a said low gas pressure; and f) using a liquefied part of the secondgas stream as the bulk of LNG produced and stored at a pressureidentical to a low pressure of gas escaping the city gate station; andis characterized by: expanding the first gas stream down to a said lowgas pressure accompanied by producing a power and deep cooling the saidfirst gas stream down to the bottom cycle temperature; using a powerproduced by the expanded first gas stream at the city gate station asaddition to a peaking power on-demand delivered to the grid by theenergy storage facility; blending the expanded first gas stream with avapor part of the second gas stream so forming a stream of low-pressuregas escaping the city gate station; and using a cold thermal energy oflow-pressure gas stream escaping the city gate station for the said deepcooling and liquefying the second gas stream and pre-cooling the wholeof delivered high-pressure gas.
 6. A method as in claims 1, 2 and 4,wherein a temperature of low-pressure gas escaping the city gate stationduring charging the energy storage facility is increased up to at leastpermissible minimum through a heat exchange between a stream of processair escaping the externally powered compressor train and a stream oflow-pressure gas escaping the city gate station.
 7. A method as inclaims 1, 3 and 5, wherein producing the LNG at the city gate stationduring discharging the energy storage facility at a pressure level belowa said low pressure of gas escaping the station includes the additionalsteps of: a) reducing a pressure of liquefied part of the second gasstream down to a required level accompanied by formation of a two-phasestream; b) separating a liquid phase from the two-phase stream with itsstoring and on-demand delivering as a salable LNG product at a requiredpressure; c) compressing a vapor phase of the two-phase stream up to alow gas pressure at the city gate outlet or up to a high gas pressure atthe station inlet, and d) mixing the compressed vapor stream with alow-pressure gas escaping the station or with a high-pressure gasdelivered to the station.
 8. A method as in claim 1, wherein ahigh-pressure gas at the inlet of city gate station is on-demand driedand ridded of the water vapor and carbon dioxide contaminants upstreamof the pre-cooling step.
 9. A method as in claims 1, 4 and 5, wherein anatural gas delivered into city gate station is on-demand subjected tofreeing from the contaminants including the steps of: a) drying thewhole of high-pressure gas upstream of the pre-cooling step; b) removingthe liquefied and/or solidified CO₂ contaminants from the first gasstream downstream of the expanding step; and c) removing the CO₂contaminants from the second gas stream upstream of the deep cooling andliquefying step.